Fancy a tricked to death 400/4

[K2-K6]

The 400 is absolute class, up to 65bhp from a motor originally producing 37bhp is an amazing hike in performance. The clutch looks really trick.
Nigel, was the original endurance racer based on a cb750sohc with a dohc top end?

Yes that 400 is fabulous, apologies to laverdaroo for way laying the thread. That era (I call it, last of the black steel frame race period) gave us some lovely design and individual styling I feel. Looks like the 400 is using original frame too.

Yes Dave,  the RCB was effectively the final development of the original SOHC 750 motor with a barrel and twin cam 16 valve head assembly on increased bore to make that motor.  Note the crankcase is the same but missing the ignition placement casting area, but wet std clutch cover and still with kickstart fitted.
They also mounted the alternator on top of gearbox to slim it overall, and notice in the first picture it's fitted with clear float bowls to carbs to give easy fault finding in endurance racing.
They did make one with gear primary drive too,  uses an idler between crank and gearbox to keep everything going in the same direction as a chain would.
The CB900 twin cam took over in race use as an adaptation of next production design from this RCB iteration.  Although you can see most of this first RCB layout mirrored in the CBX 750 motor design that came early eighties. Also why it's popular in Japan for making RCB type retro bikes. Easily into the 90s bhp wise too with a big twostroke type powerband kick to it.

[Laverdaroo]

Dont apologse in the slightest, this is turning into a 'porn' thread, I'm loving it

[Laverda Dave]

Nigel, you are an encyclopedia when it comes to engines👍. I think it's time you compiled a book (the nights are getting longer now).I always liked the look of the endurance racers, Ron Haslem used to ride the RCB didn't he? The road going RC's were always expensive and ate now going for silly money.
Talking of hotted-up 400’s, Frank has a Harrier on sale in his shop in Perivale, I think it's in the £8-10k range. I think it may be a replica, it has CR carbs fitted.

[K2-K6]

A couple more for the collection

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[MrDavo]

I wish I was allowed a camera when I was working for the Honda Superbike team at the TT. For its 50th anniversary Honda brought over a bunch of GP bikes from their museum, including a ‘six’, and as an extra bike for the Senior they had a RCB endurance racer which had been run by a French team. That was very trick in places, one detail I remember was a diaphragm on the oil tank where the oil was topped up with a big syringe, and the back wheel was arranged so the sprocket and chain stayed put while the wheel could be changed in seconds.

We were in the ex Post Office Depot in Douglas, which was open to various Honda riders as well as the BSB team, one hazard was crazy Aussies and New Zealander’s who thought it was OK to fly a remote control petrol powered helicopter around while we were trying to work. I was worried about becoming shredded if anything went wrong.

We also had the bare bones of a works 250 four from the Japanese domestic championship, that Bill Simpson spent a lot of time prepping for his son, Ian to ride. In the event the weather was so bad that it wasn’t ridden, Ian was probably only half joking when he suggested I rode it instead using his number. Joey won that race, quite unfazed by rivers running across the track. I went out with his mechanics and came back at dawn absolutely blotto.

[K2-K6]

There's a really good book covering the era, and one that I've had for years.

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Some second hand available too https://www.amazon.co.uk/Complete-Book-Endurance-Racing-Ride/dp/0854292535

It's all those details that go into these works/development bikes I find facinating as you note Mr Davo, nice to get a view of one like that close up.

[K2-K6]

The RCB development, motor architecture etc, narrow angle 16 valves, alternator above geabox, cv carbs and ultimately a gear primary drive, all in the cbx 750 design and perhaps Honda's last aircooled 750 4 ? Iteration

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Into the 90 BJP range as a 750, it came quite close to a real rcb which ran about 105 BJP from larger capacity. Rumour was development was insurance policy if the new V4 Bikes failed in market.